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Old 06-13-2012, 02:02 PM  
jmc0319
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Default Crawl space Humidity

I am looking for opinions and/or experience with either crawl space dehumidifiers with a condensate pump or power vents. I am thinking or going with one of these two options to correct the humidity issue. Any feedback will be appreciated. I am also open to other options.



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Old 06-17-2012, 07:47 AM  
joecaption
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Is there a 6 mil. plastic vaper barrier on the ground?
What's there no for venting?
Is the grade under the house lower then the grade outside?
Is there working gutters?
Are there trenches along the foundation under the house and a sump pump?

Can you post some pictures of the outside?



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Old 06-17-2012, 08:26 AM  
jmc0319
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Quote:
Originally Posted by joecaption
Is there a 6 mil. plastic vaper barrier on the ground?
What's there no for venting?
Is the grade under the house lower then the grade outside?
Is there working gutters?
Are there trenches along the foundation under the house and a sump pump?

Can you post some pictures of the outside?
Thanks. Here are the answers to your great questions:

There is a vapor barrier but it is inconsistent and does not cover the entire floor. There are large breaks in it.
There are three vents on each side of the house. However, the vents on two sides are under a brick front porch and were covered by previous home owner. The porch itself has no vents.
The grade is not lower than the outside grade.
The gutters work well and I have extensions on the down spouts to insure the water is routed away from the house.
The crawl space never actually has water in it but it definitely is very damp. At times the water pipes have condensation on them that drips.
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Old 06-17-2012, 12:21 PM  
CallMeVilla
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A dehumidifier for an open crawl space under your house? How do you "dehumidify" the open air? Forgive me on this . . . but unless you are sitting on a active water spring, I would think sealing your vapor barrier is Task #1. Finding a way to ramp up air circulation would be my next step. If that means adding vents or adding fans, I would start there.

Not my expertise but common sense is a good start! :0)

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Old 06-17-2012, 11:16 PM  
nealtw
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Run a duct from behind the porch to th side of the house and install a fan there to pull the air out. Once it's dry it may work without the fan or you could wire it to a humidistat switch.

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Old 06-18-2012, 03:35 PM  
AndyGump
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Quote:
R408.2 Openings for under-floor ventilation. The minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 150 square feet (14 m2) of under-floor area. One ventilation opening shall be within 3 feet (915 mm) of each corner of the building. Ventilation openings shall be covered for their height and width with any of the following materials provided that the least dimension of the covering shall not exceed 1/4 inch (6.4 mm):

1. Perforated sheet metal plates not less than 0.070 inch (1.8 mm) thick.

2. Expanded sheet metal plates not less than 0.047 inch (1.2 mm) thick.

3. Cast-iron grill or grating.

4. Extruded load-bearing brick vents.

5. Hardware cloth of 0.035 inch (0.89 mm) wire or heavier.

6. Corrosion-resistant wire mesh, with the least dimension being 1/8 inch (3.2 mm) thick.

Exception: The total area of ventilation openings shall be permitted to be reduced to 1/1,500 of the under-floor area where the ground surface is covered with an approved Class I vapor retarder material and the required openings are placed to provide cross ventilation of the space. The installation of operable louvers shall not be prohibited.
This is from the 2009 IRC, it may be of some benefit to you.

Andy.
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Old 06-18-2012, 04:17 PM  
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Thanks Andy

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Old 07-25-2012, 12:25 PM  
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Dehumidification of a vented crawl space is similar to running an A/C in a screened porch. It MIGHT have an effect, but it is a very, very inefficient way to work.
First, get a really, really good poly all over the floor. My advice, do this (or get a handiman to do it) and then monitor the situation.
Sounds to me like it's a poor circulation issue, and additional vents, powered, may only make it worse as moving air around by design pulls additional air in from other vents. I don't know what region you're in, but especially this time of year, more air moving in from outside means MORE humidity.
If a good poly doesn't settle things down, then seal up the crawl vents and use a dehumidifier.
Pictures would help.

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Old 07-26-2012, 09:56 AM  
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Some time back, I had a very similar problem. Like you, I thought there was no water intrusion but discovered a very small leak from my gutter downspout. This was discovered during a very hard downpour.
I sealed the hole--with very little hope of it being the problem-- and I have not had a moisture problem since. It really surprised me
I think your first step would be SURE you don't have a water entry problem.
If water is coming in, I think it would be very hard to achieve positive results even with a properly installed vapor barrier and a dehumidifier.

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Old 08-01-2012, 12:55 PM  
jmc0319
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I wanted to give an update on my crawl space issue. I had a few people come out and tell me what they think I should have done. Bottom line is that they all think I should ​remove the existing insulation under the house and install 2” thick closed-cell foam on the foundation block and band, closing in the foundation vents. Install new 6 mil poly-plastic on the ground and glue the seams and glue to the foundation wall.

Please let me know if anyone thinks this is the right approach. Based on previous feedback I think this makes sense.

Thanks.



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